In a processing laser pulse, because preferably its peak power is homogeneous from starting to ending of laser pulse output, various devises are proposed in order to obtain the homogeneous peak power.
For example, Unexamined Japanese Patent Publication No. 2006-305597 discloses a laser processing apparatus including an opening and closing unit (shutter). The opening and closing unit is disposed on an optical path of a laser beam, which is emitted from a laser emitting unit to reach a collective lens, and alternatively perform blocking and passage of the laser beam. In the laser processing apparatus, immediately before processing operation to focus the laser beam on a processing target to process the processing target, an exciting laser beam source is driven while the opening and closing unit is closed. Then, the opening and closing unit is opened to pass the laser beam on a condition that a laser medium becomes a high excitation state in which light intensity of the laser beam output from the laser medium can process the processing target. Therefore, the light intensity of the laser beam can be kept constant while power consumption is suppressed.
In a laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2004-337970, a control unit provides an initial driving current corresponding to laser output higher than a setting laser beam to an excitation unit when a line segment is marked from a starting point of each line segment using the laser beam, and then the control unit provides a driving current corresponding to the setting laser beam to the excitation unit.
In a configuration disclosed in Unexamined Japanese Patent Publication No. 2011-181761, an excitation beam condition is changed in a non-emission period by controlling a driver, whereby energy of a pulsed light beam output from a laser processing apparatus can be stabilized irrespective of a length of the non-emission period.
Unexamined Japanese Patent Publication No. 2012-248615 discloses a light amplifying device in which, based on a detection value of a peak value detector, the power (a bias current of the driver) of the excitation beam is controlled in the non-emission period such that the power is equalized between an initial output light pulse and a final output light pulse in an emission period.
In the laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2006-305597, there is a problem in that the opening and closing unit (shutter) is required to cause enlargement of the apparatus and cost increase. In a laser marking apparatus disclosed in Unexamined Japanese Patent Publication No. 2004-337970, there is a problem in that the homogeneous processing can hardly be performed because the laser output rises gradually from reference time.
On the other hand, in a laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2011-181761 and the light amplifying device and laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2012-248615, the peak power having the homogeneous laser pulse can be obtained from a beginning of laser pulse output.
However, sometimes the peak power of the laser pulse becomes unstable even in the laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2011-181761 and the light amplifying device and laser processing apparatus disclosed in Unexamined Japanese Patent Publication No. 2012-248615. Therefore, there is a demand for a configuration capable of stably outputting the laser pulse having the homogeneous peak power from the beginning of the laser pulse output.